The conversion of hydrocarbons to hydrogen and carbon monoxide containing gases is well known in the art. Examples of such processes include catalytic steam reforming, auto-thermal catalytic reforming, catalytic partial oxidation and non-catalytic partial oxidation. Each of these processes has advantages and disadvantages and produces various ratios of hydrogen and carbon monoxide, also known as synthesis gas (syngas). The present invention is directed to a catalytic partial oxidation process.
Partial oxidation processes are also well known and the art is replete with various catalytic partial oxidation processes. Partial oxidation is an exothermic reaction wherein a hydrocarbon gas, such as methane, and an oxygen-containing gas, such as air, is contacted with a catalyst at elevated temperatures to produce a reaction product containing high concentrations of hydrogen and carbon monoxide. The catalysts used in these processes are typically noble metals, such as platinum or rhodium, and other transition metals, such as nickel, all on a suitable support.
Partial oxidation processes convert hydrocarbon-containing gases, such as natural gas to hydrogen, carbon monoxide and other trace components such as carbon dioxide and water. The process is typically carried out by injecting preheated hydrocarbons and an oxygen-containing gas into a combustion chamber where oxidation of the hydrocarbons occurs with less than stoichiometric amounts of oxygen for complete combustion. This reaction is conducted at very high temperatures, such as in excess of 700° C. and often in excess of 1,000° C., and pressures up to 150 atmospheres. In some reactions, steam or carbon dioxide can also be injected into the combustion chamber to modify the synthesis gas product and to adjust the ratio of hydrogen to carbon monoxide.
More recently, partial oxidation processes have been disclosed in which the hydrocarbon gas is contacted with the oxygen-containing gas at high space velocities in the presence of a catalyst such as a metal deposited on a ceramic monolith (e.g. foam or honeycomb) support. The monolith supports are impregnated with a noble metal such as platinum, palladium or rhodium, or other transition metals such as nickel, cobalt, chromium and the like. Typically, these monolith supports are prepared from solid refractory or ceramic materials such as alumina, zirconia, magnesia and the like. During operation of these reactions, the hydrocarbon feed gases and oxygen-containing gases are initially contacted with the metal catalyst at temperatures in excess of 400° C., typically in excess of 600° C., and at a standard gas hourly space velocity (GHSV) of over 100,000 per hour.
It has been found that the most suitable fixed arrangement for the catalyst for use in the catalytic partial oxidation of hydrocarbons under conditions which would be commercially attractive is one in which the catalyst is retained in the form of reticulate monolithic structure. Catalysts for use in such a process comprise one or more catalytically active components supported on a refractory oxide carrier, the carrier being in the form of a reticulate monolith.
However, it has now been found that problems can occur in the operation of the partial oxidation process when using a reticulate monolithic catalyst. In particular, it has been found that the refractory monolithic catalyst structures are very susceptible to thermal shock and high temperature prevailing in the catalytic partial oxidation process, causing brittleness of the structure and ultimately leading to catalyst disintegration, especially when using oxygen rather than air. Accordingly, it is an objective of the present invention to provide a catalytic partial oxidation process, which combines a high level of carbon conversion to syngas with high selectivity and a high level of structural stability of the catalyst at high temperature.